Today, the performance and specification of a vehicle robbery prevention system are required to maintain the safety state of a vehicle for situations inside and outside the vehicle that is being parked. Accordingly, a recent vehicle robbery prevention system has a function of maintaining the safety of a vehicle by generating visual and auditory effects around the vehicle when various situations such as the detection of the breaking of a window for intrusion, the detection of an article robbery behavior within a vehicle, the detection of a tire theft in a vehicle that is being parked, and the detection of the illegal towaway and movement of a vehicle, are generated.
For example, Thatcham, an automotive research center of England, has organized a separate vehicle security department in order to improve vehicle robbery prevention performance and continues to move a wide variety of operations. Furthermore, Denso Corporation of Japan proposes a technology for maintaining the security of a vehicle using a robbery vehicle location tracker, an ultrasonic sensor for detecting an illegal trespasser to a vehicle, a glass breakage sensor, an inclination sensor for detecting an inclined vehicle body, and an impact sensor for detecting an impact force applied to a vehicle. Such a technology of Denso is disclosed in Korean Patent Application Publication No. 10-2005-0074324 (Jul. 18, 2005).
However, a conventional ultrasonic sensor for detecting intrusion within a vehicle is problematic in that a battery is excessively discharged in order to continuously generate ultrasonic waves. Furthermore, the ultrasonic sensor frequently erroneously detects a change in the signal, detected within a vehicle due to an external simple impact, as indoor intrusion within the vehicle. In order to prevent such a problem, in the conventional ultrasonic sensor, a signal out of a specific reception level range may be considered to be noise and removed. In such a case, a transmitting level needs to be increased by a specific level or more and maintained because receiving sensitivity from which a specific reception level range has been removed needs to maintain a specific size or more. Accordingly, there is a disadvantage in that the controllable range of the sensor is limited in controlling the receiving sensitivity of the ultrasonic sensor. Furthermore, there is a problem in that battery consumption is further increased if the receiving sensitivity maintains a specific level or more.
Furthermore, some of conventional vehicle robbery prevention devices detect the generation of an impact against a vehicle or the inclination of a vehicle using an inclination sensor or an impact sensor. In such a case, there is a problem in that the sensor sensitively responds to an external simple impact and malfunctions.